How Bang Seats Work

[paddy]

Part one as promised to Dave.

Martin Baker Mk 4 fitted to the Strikemaster.

First you need an " Oh Shit" moment to prompt you pull the handle (Seat Pan or Faceblind) After that, all things being equal, the system is totally automatic. If everything works as advertised you've done all you need to do.

My time on the Strikemaster was before the time of MDC (Miniature Detonating Cord) in the canopy so this will be the original system.

When you pull either handle the sears for the canopy jettison system and main gun are removed (Provided you have remembered to remove all the pins on preflight. Don't laugh, it's happened)

A lot from here on happens simutaneously so bear with me.

The canopy jettison cartridge fires immediately and routes hot gas to the two canopy jettison jacks on either side of the cockpit. The jacks unlock the canopy and raise the leading edge of the canopy into the airstream allowing the fast moving air to blow the canopy off. (If this doesn't happen the seat has canopy breaker horns on the top to bust through the canopy. (Once the main gun sear has been pulled you are going wether the canopy is there or not.)
Whilst the canopy jettison system is doing it's thing the clockwork (just like a model train) main gun firing unit delay mechanism is whirring through it's half second delay (Not sure wether it's 1/2 second or 1 second, it's been a long time) By the way, that whirring sound is the most terrifying thing you'll ever hear while working in a cockpit.

The firing unit then fires the main gun cartridge (About 2 inches wide and 3 inches long) The seat starts going up the rails. As this is happening (Starting from the bottom) the leg restraint lines pull tight therefore pulling the legs (via the garters on the lower legs) against the front of the seat. The riders Personal Equipment Connector (Oxygen, G Suit and Radio) automatically disconnect and emergency oxygen starts to flow.

Also during this time the actuation rods for the Drogue Gun and Barostatic Time Release unit are pulled.
As the seat rises further the two secondary seat cartridges (one 1/3 of the way up and the second 2/3 of the way up) are exposed to the hot gases and also fire. This spreads (a little) the forces that you are exposed to.
When the Drogue Gun is tripped it fires a large, heavy metal slug (About an inch in diameter and six inches long) which is attached to the Duplex Drogue System. (The Drogue Gun has killed a few Armourers that forgot to disconnect and safety pin it on seat removal)

The Drogue Gun extracts a small pilot chute which then extracts the main five foot diameter Drogue Chute (Hence Duplex Drogue)
The Duplex Drogue System is attached to the seat via The Seat Shackle which is locked by The Barostatic Time Release System.

Now you're out of the aircraft but still attached to the seat which is decelerating due to the Duplex Drogue System.
The clockwork system in the Barostatic Time Release Unit is running down it's delay. (Sorry can't remember what the delay is) and when the "G" and altitude criteria are met (Altitude is 14,000') the BTRU releases the seat harness and seat shackle. Releasing the Seat Shackle allows The Duplex Drogue System to act as a very large pilot chute for the main parachute. As the parachute starts to fill the weight of the seat causes it to fall away and the rider descends gently (relatively) to earth.

Only one more thing then we're done.
If the BTRU Doesn't release you can manually separate from the seat and open your parachute. Problem is that the Duplex Drogue System is still locked by the Seat Shackle and connected to your parachute by the Bridle Line.
To solve this the Bridle Line is routed through the Guillotine. As you manually separate from the seat a static line attached to your harness pulls yet another sear attached to the Guillotine which fires another cartridge which propels a cutter which (you guessed it) cuts the Bridle Line.

This is the basics of how all Martin Baker Automatic Seats work.
Add in some optional extras like rocket packs and there you have it.

Questions and corrections are most welcome.

Next the IC3 and IG3 Escapac seats fitted to the Skyhawks.

[beagle]

MBEU6011BA for para assy from memory.

best thing that happens is at 5pm the next day when the pilot whom ejected, if he is permitted to leave medical arrives via the mess with a 50lt keg.

[jonesy]

Excellent insight. Was that from memory or the manual?

[phil]

I imagine it was from memory. I can still recite the firing sequence of the Mk10, which is very similar of course.

[paddy]

Oct 5, 2011 20:08:33 GMT 12 jonesy said:

Excellent insight. Was that from memory or the manual?

Memory of course.

It's probably somewhere on Wikipedia

[beagle]

he has the NZAP beside his bed

[paddy]

IC3 in the A4K

First have your "Oh Shit" moment.

Pull either handle. The first thing that happens is the Canopy Jettison Cartridge fires. It's on zero delay as is the RoCat Cart. At this point in time however the RoCat (Rocket Catapult) cartridge can't fire until the canopy is jettisoned. With the Skyhawk, if the canopy doesn't go you aren't going either.

When the canopy jettison cart fires it ruptures a high pressure nitrogen resevoir which is attached to the canopy bungie. This causes the bungie to deform and metal bars around the bungie also deform and thus (by a mechanical linkage) unlocks the canopy. The excess pressure in the bungie then blows the canopy from the aircraft.

This removes the canopy seat interface and allows the RoCat cartridge to fire.
This ignites the Rocat and you're on your way.

As the seat rises the PEC disconnects, Emergency Oxygen starts to flow and the SARBE Beacon starts it's noise. Also, the Man Seat Separation cartridge fires and starts it's time delay (and no I can't remember what that delay is either) There is no clockwork in this seat, it's all explosives. That makes the seat about 1/4 the weight of the Marin Baker Seats.

Being sent up the rails by a rocket results in a far more gentle acceleration (relatively) than the Martin Baker Seats hopefully resulting in less injury for you, the rider.

Now the Escapac seat is designed to throw you forward of the aircraft and, to that end the rocket nozzle is canted back at a 45 degree angle.
With the Martin Baker Seats there is no acceleration once the seat has left the rails. With the Escapac the rocket motor is still burning when the seat leaves the rails. Can you see the problem with a canted still burning rocket and no rails to restrain it. The seat will spin backward like a giant catherine wheel.
The clever people at Douglas came up with a really nifty system to stop this called " The DART" (Directional Automatic Re-alignment of Trajectory. Don't you just love aircraft acronyms.)
The DART consists of about twenty feet of 1 inch tubular nylon cord attached to the cockpit floor and running through two heavy duty brakes on the base of the seat. This keeps the base of the seat down and stops the catherine wheel effect. When it runs out it merely slips through the brake and remains with the aircraft. (Those of you that have seen photos of 07 after Fred left it to it's own devices can see the Dart Line lying over the cockpit)

So now you're out of the cockpit, the rocket has burnt out and you are still in the seat. The Time delay Cart for the Man Seat separation has just burnt through it's time delay and fires the actual Man Seat Separation Cartridge. This forces a piston up which, while on it's way up, unlocks the seat harness. When it reaches the top of it's travel it ruptures yet another nitrogen resevoir which inflates the two separation bladders (One in the seat pan and the other in the seat back thereby forcing the seat away from you.
You are now in freefall and the only thing between you and a rather messy meeting with the ground is the Automatic Parachute Opener packed in the parachute container or your trusty right hand. (To pull the ripcord)

With the IG Seat, the only difference (From an Armourers point of view) is the Man Seat Separation. There are no longer a nitrogen resevoir or separation bladders. There is, however, a separation rocket on the port side (top) of the seat. (Also called the Ear Burner)

The Time delay Cart for the Man Seat separation has just burnt through it's time delay and fires the actual Man Seat Separation Cartridge. This forces a piston up which, while on it's way up, unlocks the seat harness and routes the residual hot gas to the Ear Burner which also pushes the seat away from you.

The other differences are in the parachute which has a stabilisation drogue for the freefall part of your descent and a Ballistic Speader to make the canopy open faster. Since Armourers did not play with these bits I don't have much knowledge of them. They were a Safety and Surface toy and Dave would have far more knowledge of them.

Next, the TA4K. (Don't expect such a precise post as there are 20 to 30 cartridges in that system and it took me a week of my Mechs course to get it in my head and time is not your head's friend)

[paddy]

Oct 5, 2011 20:08:33 GMT 12 jonesy said:

Excellent insight. Was that from memory or the manual?

It was from the amazing training we all received from the various TTS's in the RNZAF.

I have never had training of that quality either before or since my time in the RNZAF.

[Dave Homewood]

Good thread Paddy. I agree about the quality of training, it was first class.

[skyhawkdon]

I'll second that. It never ceases to amaze me how much we can still remember about the aircraft systems after all these years (and from memory too!).

[paddy]

Now for the TA4K

The seats work exactly the same. The only difference is in the Canopy Jettison System and in the sequencing.

In the TA4 there is an option for command ejection. This is controlled by a valve that has two positions: Either Aircrew can eject both or Front Aircrew can eject both and rear can eject themselves only. The latter was the default setting in the TA4K and was lockwired as such.

I'll deal with Canopy Jettison first. When Canopy Jettison is initiated (Either by pulling either seat handle, either internal Canopy Jettison handle or either external Canopy Jettison handle) hot gas is routed to the Canopy Jettison charge on the top of the canopy ram and the canopy is blown off. Simultaneously hot gas is routed to a valve controlling hydraulic pressure to the canopy ram and cuts it off. This is to stop the ram rising once the weight of the canopy is gone. If the ram rises this will have obvious ramifications to the ejectee in the back.
As per the A4 there is an interlock between the canopy and seat initiation. If the canopy hasn't gone the seats aren't going either. (As an aside to this, if the external Canopy Jettison handle is pulled this also removes the interlock. So you now have a live seat with 3 levels of protection gone. ie: Headknocker up, Seat Pins stowed and Canopy Interlock gone)

Sequencing: Those of you that paid attention to my previous post on the A4K will know that the RoCat nozzle is canted back at a 45 degree angle. If the front seat goes first this will have even more serious ramifications to the rear seat occupant so, therefore the rear seat MUST go first. (Even if it's empty)
If the rear occupant initiates ejection the canopy is jettisoned as above and the seat works as previously described. The front occupant, unless they also eject, is now left cruising with the top down.

Now is when it gets complicated. (Remember this is memory 35 years old so be gentle with me)

If the front occupant initiates ejection his Canopy Jettison cartridge fires and removes the canopy as previously described. Hot gas travels from the front cockpit and initiates the rear seats RoCat. (I can't remember how the Canopy Jettison interlink works in this case but, be assured, it does)

The front seat is now free to fire (Again, wether this is by a mechanical interlink or a timed cartridge I can't remember)

The seat rises up the rails and Barnsey is FREE.

As yet another aside, in that technically accurate movie "Top Gun" Goose couldn't been killed by colliding with the canopy on ejection unless the canopy seat interlock had totally failed.

If anyone wants to know any other secret Armourer's business you only have to ask.

[skyhawkdon]

Well done that man, exactly as I remember it! Incidently the T-bird Command Ejection selector switch was know as the "Chicken Switch" for obvious reasons! I don't have a photo of it but will have to see if I can get one from '54 at Wigram.

[skyhawkdon]

A photo speaks a thousand words, so here is a video of the Douglas T-bird zero-zero ejection trials showing the sequence of canopy jettison, rear seat firing followed by front seat firing. Note the trajectory of the seats - 45 degrees forward and up and not much seperation between the seats! Then there is footage of an early A-4 sledge test ejection using a dummy showing man-seat separation (looks like the old bladder system) and parachute deployment (pre-ballistic spreader).

[jonesy]

Whats also amazing is the sequences that it goes thru to initiate ejection. Makes ya wonder how they came up with them, and if it was thru trial and error...

[E.T.]

Nov 1, 2011 17:02:06 GMT 12 paddy said:

Now for the TA4K
If the rear occupant initiates ejection the canopy is jettisoned as above and the seat works as previously described. The front occupant, unless they also eject, is now left cruising with the top down.

I think it was Wg Cdr Donaldson was it that was subjected to this experience when flying with the Yanks and his back seat instructor suffered a bird-strike and ejected leaving him flying solo???

Nov 1, 2011 17:02:06 GMT 12 paddy said:

If anyone wants to know any other secret Armourer's business you only have to ask.

Sooooo tempting!!! So much of the after-hours stuff that didn't seem to have any logic so must have been due to "secret Armourer business". I did get a wee insight to some of it when Runny's Tech Cse was put in the same accomm as us poor CET Mechs during their Av phase at Wigram. :-)

[obiwan27]

E.T. I think you might find that it was Donaldson that was the instructor, the aircraft suffered the birdstrike in the area of the cockpit where he was sitting. He was blinded and disorientated but decided to punch out, leaving the student in the aircraft to eventually land it safely.

More here: www.stuff.co.nz/sunday-star-times/features/3192692/Drama-in-the-skies

[mumbles]

Nov 1, 2011 17:02:06 GMT 12 paddy said:

As yet another aside, in that technically accurate movie "Top Gun" Goose couldn't been killed by colliding with the canopy on ejection unless the canopy seat interlock had totally failed.

Sorry to be picky, but that was included in the movie precisely because it did happen to someone earlier in the career of the F-14 (source USN technical advisors to the movie among others).
The producers wanted an ejection incident that would kill Goose but leave Maverick unharmed, so based it on an F-14 accident that occured in the late 70's in similar circumstances. I understand the incident led to a revision of the ejection sequence to prevent a recurrence, so it may not have been accurate for the era of the movie, but did happen once.

[skyhawkdon]

Some info on the "Chicken Switch" from Phil Thompson below:

[oldgunny]

As an insight to the ejection sequence of the TA-4, if for some reason the back seat failed to bang out, there was nothing to stop the front seat from going. This meant anyone in the back seat was subjected to the rocket blast of the front seat, and still had to manually separate from the aircraft, if there was time, if he was still able to.